1. Field of the Invention
The present invention relates to dye compositions used for colorimetric determination of a chemical or biochemical component (analyte) in an aqueous fluid, such as blood. In particular, the present invention relates to the field of dry reagent matrix compositions for use on test strips adapted to receive a liquid sample of body fluid whereby a dye indicator composition wetted by the fluid reacts with an analyte in the body fluid and provides a visual or color indication of the presence or concentration of the analyte.
2. State of the Art
Indicator compositions for use in devices for color indication of various analytes in liquid samples, such as body fluids, are well known in the art and are embodied in numerous commercial products, such as dry reagent test strips. In such test strips, a dye or dye couple composition is typically formulated in a solution which is applied to a test strip matrix and then dried to form a dry chemistry reagent system on the test strip. The dry chemistry reagent system commonly involves an oxidizable dye or dye couple composition in combination with a oxidase or peroxidase specific for the analyte to be tested. When the dry chemistry reagent system is contacted with a liquid sample containing the analyte, the analyte reacts with its corresponding oxidase or peroxidase producing hydrogen peroxide which in turn oxidizes the dye or dye couple to produce the desired color change thereby indicating the presence or concentration of the analyte.
Example of such dry chemistry reagent systems are disclosed by Phillips et al. in U.S. Pat. Nos. 4,734,360; 5,059,394 and 5,304,468; by Yu in U.S. Pat. No. 5,453,360; Hoenes in U.S. Pat. No. 5,334,508 and by Hochstrasser in U.S. Pat. Nos. 3,964,871 and 4,059,407. The disclosures of these patents are incorporated herein by reference in their entirety.
A number of dry chemistry reagent systems have been incorporated into various commercial products. While such products generally provide acceptable indication and testing under some conditions, certain problems exist with prior dry chemistry systems. For example, in some dry chemistry reagent systems, the dye components tend to sublime over time from the test strip so that when the test strip is used by the consumer it may not provide an accurate indication. This problem limits the shelf life of the test strips.
Additionally, in some dry chemistry reagent systems, the color change provided by the dye or dye couple components continues to change over time rather than reaching a stable end point. When such dye systems are employed, the color indication must be accurately read at specific time intervals in order to obtain an accurate indication of the presence or concentration of an analyte.
Moreover, some dry chemistry reagent systems require a low pH to provide the necessary stability for the dye or dye couple system. However, the pH of such systems is often below the desired pH level for stability of the enzyme used in the dry chemistry system. Therefore, the amount of enzyme employed in the formulation must be increased to compensate for the enzyme's instability, thus increasing the cost of the dry chemistry reagent system. Additionally, when the enzyme is used under non-optimal pH conditions, the enzyme may give undesired or false indications of the presence or concentration of the analyte.
Finally, in some dye or dye couple systems, the optimum wavelength for determining the presence or concentration of an analyte is often obscured or interfered with by components of the body fluid being analyzed, such as hemoglobin.
In view of the above, it is an object of this invention to provide a dry chemistry reagent system having improved stability regarding sublimation of the dye or dye couple system from the dry chemistry test strips.
It is also an object of this invention to provide a dry chemistry reagent system which rapidly produces a stable end point in a short period of time thus eliminating the time dependent measurements or determinations by the user.
It is a further object of this invention to provide a dry chemistry reagent system which can be formulated and used at a pH range more closely approximating physiological pH thus providing a more stable system for the enzyme or enzymes employed in the manufacture and use of the dry chemistry system.
It is a still further object of this invention to provide a dry chemistry reagent system which permits an accurate determination of the presence or concentration of an analyte in a body fluid without significant spectral interference by components of the body fluid being tested.
The above objects as well as others are achieved by the compositions, devices and methods of this invention as disclosed herein.